1. Field of the Invention
This invention relates to a panel assembled tank and more particularly to a panel assembled tank consisting of high pressure resistant square panels made of reinforced plastic and having high watertight and high pressure resistance.
2. Description of the Prior Art
There have been used a great number of tanks of various kinds, shapes and constructions settled at high levels as on roofs of high buildings. In this case, panel assembled tanks manufactured by a number of unit panels having peripheral edges of square wall surfaces folded to form securing flanges for connecting together the unit panels and require only unit panels necessary to assemble the tanks no matter how large the volume of the tank may be. Such unit panels are particularly preferable for manufacturing tanks to be set at high positions because the kinds of unit panels can be limited to a small number which is suitable for mass-production.
Reinforced plastics have been preferably used for the material of the unit panels. With large assembled tanks, however, there are many problems to be solved as to pressure resistance and watertightness. For example, the inner pressure of water filling the tank causes the panels and their walls to bulge outwardly. In order to mitigate the bulge in the panels, it has been suggested to form the panel with a protrusion in the form of a pyramid or truncated pyramid as explained later in connection with the drawings.
In the event that the thus formed panel having a uniform thickness and is fixed at its periphery is subjected to an inner pressure, stresses will concentrate at corners of the panel or at the bottoms of the securing flanges to cause partial failure or breakdown thereat.
With a large assembled tank, the bulging of the side walls as a whole caused by the inner pressure can not be avoided and the increased weight of the ceiling wall requires a reinforcement to support the weight which reinforcement may generally be columns. Furthermore, such columns must be worked at their ends so as to meet the shape of the bottom wall and require mounting members for setting the columns onto the bottom wall of the tank.
It is desired to reinforce the opposite side walls of the tank by means of tie rods connecting the side walls in order to restrain the bulging of the side walls as a whole to a minimum. In fact, however, it is no easy matter to assemble the panels to form a tank by rigidly clamping the tire rods to the side wall panels and to provide complete watertightness at the connections of the tie rods to the panels when the tank is filled with water in a manner that the tie rods are effectively subjected to tensile forces without undue forces acting upon the unit panels.
The bottom wall panels of the assembled tank are generally intended to resist the inner pressure by supporting tensile stresses. In other words, the panels commonly have protrusion portions extending out of the tank. Consequently, there is a tendency for connections between the panels to open away from each other resulting in less watertightness. With such panels, the cleaning of the inside of the tank is apt to be insufficient because there are recesses forming pools of water in the tank at the back of the outwardly extending protrusions of the panels.
These assembled tanks require piping for pumping and supplying water. The configuration of the panels having the pyramidal protrusions makes it difficult to provide the piping and requires particular attachments for connecting pipes to the oblique surfaces of the protrusions which may increase the cost of the tank even if they improve the accuracy of connecting the pipes. A square panel formed by a truncated pyramid having a flat center surface area can avoid the need for special attachment for the piping. In this case, however, the position of the piping is invariably at the center of the panel corresponding to the top of the truncated pyramid, so that the effective water level of the tank is unavoidably limited to a small value.
Moreover, sealing materials are generally positioned between the flanges of the panels for the purpose of preventing leakage at the connections. Dimensional errors of the assembled tank resulting from the sealing material which is generally deformable, may often cause extra cost in setting the tank in place.
Furthermore, when the assembled tank is used for holding a water supply, there is a danger of damage to the tank by the dynamic water pressure resulting from the oscillation of water caused by an earthquake.